Abstract Aplysia californica is a unique animal model contributing to groundbreaking discoveries in basic neurophysiology as well as the cellular basis of memory and learning. The genome of Aplysia has been sequenced and extensive genome and transcriptome resources are available, facilitating a wide variety of gene expression studies. Aplysia is also an outstanding model for studies of aging, with an annual lifecycle marked by significant behavioral, neurophysiological and transcriptomic hallmarks progressing to senescence and death. The overarching goals of the National Resource for Aplysia at the University of Miami (the Resource) are to produce and distribute consistently high-quality cultured California sea hares, A. californica, at all life stages for biomedical research and education, and to improve and expand the usefulness of this model system to the biomedical community. The goal of this application for supplemental support is to investigate the distribution and potential for pathology of a newly discovered, naturally occurring, nidovirus infection in Aplysia, Aplysia abyssovirus 1 (AAbV). Investigation of AAbV is directly relevant to the aims of the parent P40 grant: a key component of aim 1 of the parent grant is to monitor the health status of animals at the resource and to this end, limited monitoring of AAbV in hatchery animals has already been underway for the past year (with preliminary data presented here). Thus, the experiments proposed here clearly fit within the scope of aim 1 of the parent grant. The proposed studies would allow us to address important biosecurity concerns regarding the distribution and effects of AAbV that could not be supported by the parent grant alone. We propose two primary aims: 1. Development of improved testing and AAbV-free animals and 2. Assessment of pathology associated with AAbV. In aim 1 we will develop several methods for non-invasive monitoring of AAbV levels in Aplysia including hemolymph samples, gill swabs, fecal samples, and water samples. Theses methods will allow us to identify uninfected animals in cohorts while culling infected animals. An additional, major goal of this aim will be to create a consistent and reliable supply of AAbV-free (SPF) animals. Aim 2 will follow three discrete approaches to understand the pathology of AAbV infection by examining changes in gene expression and tissue ultrastructure associated with high viral loads. In this aim we will also investigate developmental impacts of AAbV on embryos and larvae.